1. Field
Implementations described herein relate generally to laser-based image-generating systems and, more specifically, to a method of tile row pixel shift in a tiled display system.
2. Description of the Related Art
Electronic display systems are commonly used to display information from computers and other sources. Typical display systems range in size from small displays used in mobile devices to very large displays, such as tiled displays, that are used to display images to thousands of viewers at one time. Tiled display systems are generally made up of multiple smaller individual display devices, or “tiles”, that are carefully aligned when assembled to provide a seamless and uniform appearance. In some implementations, each tile may include a self-contained laser-based image-generating system.
In laser-based image-generating systems, a rotating polygon mirror is commonly used to scan one or multiple laser beams across an image-generating surface, such as the phosphor screen of a laser-phosphor display. A rotating polygon mirror is a multi-faceted optical element having a plurality of reflective surfaces. A laser beam incident on one of the reflective surfaces is directed to the image-generating surface, and as the polygon rotates, the incident laser beam sweeps across the image-generating surface, thereby producing one line of an image on the image-generating surface.
In some devices, a specialized rotating polygon mirror, known as a raster polygon mirror, is used to produce 2-dimensional scanning of lasers across the image-generating surface. In a raster polygon mirror, each reflective surface is canted at a different angle. As with a rotating polygon mirror, when the raster polygon mirror rotates, a laser beam incident on a reflective surface of the raster polygon beam sweeps across the image-generating surface to produce a line of an image on the image-generating surface. However, as each subsequent reflective surface rotates through the incident laser beam, the beam is directed to and sweeps across a different location on the image-generating surface, thereby performing 2-dimensional scanning of the laser across the image-generating surface. Thus, a raster polygon mirror allows a laser to be scanned across a 2-dimensional surface using a single moving component, thereby facilitating high-speed laser imaging technologies.
A drawback to using a raster polygon mirror for scanning lasers across an image-generating surface is that there is a substantial time delay between the scanning of the first portion of a 2-dimensional surface and the scanning of the final portion of the 2-dimensional surface. Consequently, when displaying a video of an object moving across the screen that is moving fast enough and is located on two or more tiles, a “Christmas tree” or “stair step” effect can be seen. One example of the Christmas tree effect is illustrated in FIG. 1.
FIG. 1 illustrates a portion of a tiled display system 100 that displays an elongated object 150 that is moving horizontally in direction 102 across three display tiles 121, 122, and 123. Each of display tiles 121, 122, and 123 displays an image by rastering lasers horizontally across the surface of the respective display tile using a rotating raster polygon mirror. Because of this, there is a discrete time delay between when a top portion and a bottom portion of elongated object 150 is produced on each of display tiles 121, 122, and 123. For example, the delay can be on the order of several milliseconds. When elongated object 150 is moving across tiled display system 100 at a high enough speed, elongated object 150 covers a distance 160 during such a time delay that is noticeable to a viewer of tiled display system 100. Thus, a segment 151 of elongated object 150 that is displayed by display tile 121, a top portion 151A and a bottom portion 151B of segment 151 appear to the viewer to be positioned as shown relative to each other, with bottom portion 151B trailing top portion 151A by distance 160. While elongated object 150 is not actually drawn diagonally, there is such an appearance because the viewer's eyes are moving while tracking the motion of elongated object 150. Similarly, a bottom portion 152B trails a top portion 152A of a segment 152 by distance 160 and a bottom portion 153B trails a top portion 153A of a segment 153 by distance 160. Consequently, the rendering of moving elongated object on tiled display system 100 appears to have a “stair step” because the image pixels on top portion 152A of segment 152 appears to lead the image pixels of bottom portion 151B of segment 151. A similar effect is in evidence between display tiles 122 and 123.
Depending upon the electronics and raster scan times, the above-described phenomenon may reveal itself in other display systems as well, especially when such display systems are large. Furthermore, such an effect may even be present in a liquid crystal display as the first pixel of a top row actually receives signal before the last pixel of the bottom row for imaging.
As the foregoing illustrates, there is a need in the art for a time-sequenced, segmented display system that can display moving objects without the Christmas tree or stair step effect.